1. Field of the Invention
The invention relates generally to method and apparatus for ultrasonic testing of generally uniform cross-section elongate goods and, more particularly, but not by way of limitation, it relates to improved apparatus for defect detection in tubular goods such as oil well casing, drill pipe, tubing and the like.
2. Description of the Prior Art
The prior art includes numerous methods and varying forms of apparatus for ultrasonic testing of metallic objects or specimens, and such prior devices have functioned under a variety of techniques and energy coupling schemes to provide defect and/or discontinuity indication of the test specimens. It is only recently that attempts have been made to carry out large-scale ultrasonic testing of oil field tubular goods and particularly those methods which carry out the test operation with controlled relative movement between the testing cell and the specimen goods.
A prior U.S. Pat. No. 4,106,347 discloses use of a frame including a quadrature array of extendable cylinders for moving wheeled crystal transducer assemblies into contact with a drill pipe section at a position above the derrick floor during tripping operations. In this disclosure, four transducers functioning within water filled rubber wheels are maintained in contact with selected portions of the drill pipe in order to read any defects. Such systems must contend with extraneous readout of confusing nature due to interposition of diverse materials, such as the energy coupler and the rubber wheel container structure, prior to transmission of the ultrasonic energy into the specimen tubular goods. Direct normal positioning of the energy transducers further imposes limitations as to types and positions of defects that are detectable.
U.S. Pat. No. 3,533,281 discloses another form of ultrasonic testing wherein the plural ultrasonic energy transducers are rotated relative to the tubular goods undergoing test as it is moved longitudinally relative to the test section. Here again, ultrasonic energy transducers are aligned directly normal to the tubular goods and thus enable only a single testing mode of the specimen material. U.S. Pat. No. 3,540,267 discloses yet another form of drill pipe testing device wherein the drill pipe is rotated and/or flexed during testing to provide tension and compression stressing during inspection by relatively conventional ultrasonic energy transducer assemblies.